Es are not better than Cs. Ds are not better than Cs or better than Es etc. Certainly not from a value perspective.
If anything I would suggest you try to find out the ACTUAL weight per tire for the model and size you are looking at.
Looking at 33" sized tires:
My General Grabber AT2s 285x75x16 are 59 lbs per tire and rated D
BFG TAs 285x75x16 / 33s are ~ 55 lbs per and rated E
then looking at 31.5 - 32" tires
* General Grabber AT2s 265x75x16 (31.5") are 53 lbs per tire and rated E only
* Cooper Discover STT 265x75x16 (31.5") are
41 lbs per tire, off road rated and come in load range C.
Cooper Tire & Rubber Company - Discoverer STT PRO?
Consider that the stock tires probably did not weigh more than 40 lbs per tire. Now consider you are pushing a tire weighing 59 lbs. That is nearly 50% increase in weight per wheel. It does matter!
I've got the bigger 285s (@ 32.8") but I'd consider going back to the 31.5 and in a much lighter tire in a heartbeat. In fact my friend just bought a set of those lighter weight Cooper Discover tires. He has a Toyota as well. Perhaps down the road I can convince him to let me try them out for a for a few days.